"do" not needed for side-effects in functions

Author: jig

dolessfn_test.go

@@ -0,0 +1,47 @@
+package lisp_test
+
+import (
+	"context"
+	_ "embed"
+	"log"
+	"testing"
+
+	"github.com/jig/lisp"
+	"github.com/jig/lisp/env"
+	"github.com/jig/lisp/lib/core/nscore"
+	"github.com/jig/lisp/types"
+)
+
+//go:embed dolessfn_test.lisp
+var dolessfn_test string
+
+func TestDoLessFunction(t *testing.T) {
+	ns := env.NewEnv()
+	for _, library := range []struct {
+		name string
+		load func(ns types.EnvType) error
+	}{
+		{"core mal", nscore.Load},
+		// {"core mal with input", nscore.LoadInput},
+		// {"command line args", nscore.LoadCmdLineArgs},
+		// {"concurrent", nsconcurrent.Load},
+		// {"core mal extended", nscoreextended.Load},
+		// {"assert", nsassert.Load},
+	} {
+		if err := library.load(ns); err != nil {
+			log.Fatalf("Library Load Error: %v\n", err)
+		}
+	}
+
+	ast, err := lisp.READ(dolessfn_test, nil, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	res, err := lisp.EVAL(context.Background(), ast, ns)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !res.(bool) {
+		t.Fatalf(`res.(int) != 4 (res.(int) == %d)`, res)
+	}
+}

dolessfn_test.lisp

@@ -0,0 +1,8 @@
+(do
+    (def sum-with-sideeffects (fn [x y]
+        ;; this area is executed only for side effects
+        (- 1 1)
+        ;; This is returns the value of the function
+        (+ x y)))
+    (assert (= 7 (sum-with-sideeffects 3 4)))
+    true)

mal.go

@@ -567,7 +567,7 @@ func EVAL(ctx context.Context, ast MalType, env EnvType) (res MalType, e error)
 		case "fn":
 			fn := MalFunc{
 				Eval:    EVAL,
-				Exp:     a2,
+				Exp:     List{Val: append([]MalType{Symbol{Val: "do"}}, ast.(List).Val[2:]...)},
 				Env:     env,
 				Params:  a1,
 				IsMacro: false,